Summary: A chemo-electro-mechanical mathematical model
for simulation of pH sensitive hydrogels
Sudipto K. De, N.R. Aluru *
Beckman Institute for Advanced Science and Technology, University of Illinois at Urbana-Champaign,
405 N. Mathews Avenue, Urbana, IL 61801, USA
Received 16 May 2002; received in revised form 8 November 2002
Abstract
Hydrogels are networked structures of polymer chains cross-linked to each other and surrounded by an aqueous
solution. The gels swell/deswell under several environmental conditions like pH, salt concentration, temperature,
electric field, light etc. Minor modifications can also make them sensitive to several biological agents. As a result, there
is a widespread application of hydrogels in a number of areas like control of microfluidic flow, development of muscle-
like actuators, filtration/separation, MEMS/Bio-MEMS and drug delivery. This makes it important to properly un-
derstand these materials. In this paper, we present an improved mathematical model (see [J. Microelectromech. Syst.
11(5) (2002) 544] for details on the earlier model) to predict the swelling/deswelling rates of hydrogels in buffered pH
solutions. The kinetic model developed earlier neglected the electro-static effects within the gel generated due to the
movement of the ions. It also used the Donnan theory which may not be valid in the interior of the gel. The present
work takes into account the electro-static effects and replaces the Donnan theory with the more general chemo-electro-
mechanical model. Time dependent mechanical equations and the effect of fluid flow velocity have also been explored in
the new models. The results have been compared with experimental data and a significant improvement has been
noticed after the above modifications were made, especially for smaller gel sizes.